Freestanding graphene/MnO₂ cathodes for Li-ion batteries

Abstract

Different polymorphs of MnO2 (α-, β-, and γ-) were produced by microwave hydrothermal synthesis, and graphene oxide (GO) nanosheets were prepared by oxidation of graphite using a modified Hummers’ method. Freestanding graphene/MnO2 cathodes were manufactured through a vacuum filtration process. The structure of the graphene/MnO2 nanocomposites was characterized using X-ray diffraction (XRD) and Raman spectroscopy. The surface and cross-sectional morphologies of freestanding cathodes were investigated by scanning electron microcopy (SEM). The charge–discharge profile of the cathodes was tested between 1.5 V and 4.5 V at a constant current of 0.1 mA cm−2 using CR2016 coin cells. The initial specific capacity of graphene/α-, β-, and γ-MnO2 freestanding cathodes was found to be 321 mAhg−1, 198 mAhg−1, and 251 mAhg−1, respectively. Finally, the graphene/α-MnO2 cathode displayed the best cycling performance due to the low charge transfer resistance and higher electrochemical reaction behavior. Graphene/α-MnO2 freestanding cathodes exhibited a specific capacity of 229 mAhg−1 after 200 cycles with 72% capacity retention.

Binary Fe/Mn-Based Nanocomposites as Li-Free Cathode Materials for Li Batteries Assembled in Charged State

“…The first cycle charge delivered a capacity of 540 mAh/g (Figure a). The observed differences in first cycle charge and discharge capacity for cathode materials are not expected but have been observed previously. − However, this observation is rarely discussed. Sometimes, the first cycle charge–discharge capacity or all charge capacity are omitted in the capacity versus number cycle plots in the literature. − Here, we would like to propose plausible explanations.…”

“…The observed differences in first cycle charge and discharge capacity for cathode materials are not expected but have been observed previously. − However, this observation is rarely discussed. Sometimes, the first cycle charge–discharge capacity or all charge capacity are omitted in the capacity versus number cycle plots in the literature. − Here, we would like to propose plausible explanations. One of the possible reasons of the observed difference in first cycle could be attributed accident partial discharge in cell assembly process before testing, since the cells were assembled in the charged state.…”

Freestanding and Flexible β-MnO2@Carbon Sheet for Application as a Highly Sensitive Dimethyl Methylphosphonate Sensor

“…After the redox chemical reaction step, peaks associated with the crystallinity of MnO 2 did not appear in the MnO 2 -PPy@PAN, whereas in the β-MnO 2 @CNF spectrum, characteristic diffraction peaks at 2θ angles of 34.98, 40.60, and 58.72° corresponding to the (110), (101), and (211) planes of β-MnO 2 were observed. , In addition, Figure b exhibits Raman spectra in the range 200–2500 cm –1 of the CNF sheets without and with MnO 2 decoration. The typical β-MnO 2 peaks at 650 cm –1 indicate the stretching mode of octahedral MnO 6 , and two weak peaks at 362 and 302 cm –1 originate from the bending mode of O–Mn–O or Mn 3 O 4 as a minor portion of Mn 2 O 3 . , Energy-dispersive X-ray spectroscopy (EDX) element mapping analysis also confirmed that Mn and N were uniformly distributed along the surface of an individual nanofiber in the sheet structure (Figure ).…”

A novel β-MnO2and carbon nanotube composite with potent electrochemical properties synthesized using a microwave-assisted method for use in supercapacitor electrodes

“…2, the diffraction peaks of the pure β-MnO 2 were at 28.6°, 37.3°, 40.9°, 42.8°, 46.1°, 56.7°, 59.4°, 64.8°, 66.8°, 67.3° and 72.3°, corresponding to (110), (101), (200), (111), (210), (211), (220), (002), (310), and (112) planes, respectively. 58–60 There were no other peaks that resembled different phases or impurities. The XRD pattern of β-MnO 2 /CNTs closely resembled the β-MnO 2 reference spectrum.…”